import machine as esp32
import time

def knightrider_leds(start, stop, step):

    for i in range(start, stop, step):
        led_flash(led_pins[i])

def led_flash(pin_no):

    led = esp32.Pin(pin_no, esp32.Pin.OUT)
    led.value(1)
    time.sleep(0.2)
    led.value(0)

led_pins = [21, 22, 27, 23, 26, 25]

while True:
    knightrider_leds(0, len(led_pins), 1)
    knightrider_leds(len(led_pins)-2, 0, -1)